I don't know Madrid as well, but I can say that the places you've chosen in San Sebastian and Barcelona are all very nice. In fact, they're all pretty fancy. I wonder if you're depriving yourself of the more casual, authentic eats in Barcelona and SS. The tapas places in SS are great -- Txpetxa is my favorite. And Barcelona has little places in La Boqueria (Bar Pinotxo, for example) and Cal Pep. And you have to save room for a meringue at the La Colmena bakery.

I agree that MB and Etxebarri is alot for one day, if you plan on the tasting menus at both. Since you are going to Barcelona I would suggest going to Lasarte which is also a Martin Berasategui restaurant and is a Michelin 2 star.

Heeney is partially correct - Extebarri is only open for dinner Saturday night, and closed Mondays. By the way Cinq Sentis is my favorite restaurant in Barcelona proper, so hope you enjoy the experience.